This invention pertains to electrostatic printing machines and more particularly to an improved web-developing system and method for same featuring an improved toner fountain recovery system.
In general, in some electrostatic printing machines, an elongate web of material is moved in a predetermined path where, at one station, portions of the surface of the web will be electrostatically charged to create a pre-recorded latent image on the web. Thereafter, the latent image is developed in response to application of toner material thereto. In one arrangement, the web passes in close proximity across the top of a toner fountain in which liquid toner is pumped to overflow the side edges of the fountain and spill into a catch basin disposed around the toner fountain for return to a reservoir.
One example of such a toner fountain is shown in U.S. Pat. No. 3,729,123, issued Apr. 24, 1973.
In apparatus of the kind described, the printing web is wetted by toner as it is drawn across the toner fountain. Means are provided for physically removing first the bulk or main portion of the liquid toner and then the remainder thereby "drying" the web.
As disclosed herein, vacuum means operating with a degree of suction responsive to the flow rate of the toner supplied to the toner fountain serves to recover the remainder portion of the liquid toner and to return it to a toner reservoir.